The invention relates to the artificially induced flow of venous blood in a human leg which, for one reason or another, may be impaired, in that normal processes associated with normal walking are either inadequate or not available to the patient.
In our pending patent applications, Ser. Nos. 621,499 and 763,686 (said applications being herein incorporated by reference), we disclose inflatable bladder or cuff means for promoting return flow of venous blood, by pulsed compression of the blood vessels within the plantar arch, the same being accomplished by transient flattening the plantar arch and/or by transient upward application of squeezing force against the sole of the foot. In either case, the action is localized between the ball and the heel of the foot. In the case of flattening the plantar arch, spreading force is directed at and between the ball and heel of the foot; in the other case, the sole of the foot is squeezed upward against the underside of reacting metatarsal and tarsal bone structure.
In normal walking, the foot is intermittently weight-bearing, as a result of which the involved plantar arch is transiently flattened and foot-pump action proceeds, with little or no muscular intervention. The devices and methods of said patent applications are operative to produce foot-pump action in non-weight-bearing circumstances, as when the patient is bedridden or the leg is in a cast.
Effective as our foot-pump actuating method and bladder devices may be, the fact remains that such actuation of the foot pump alone will not fully duplicate the pumping cycle which is the result of normal walking, for the reason that, although the foot pump is the primary pump in the leg, there are two further pumps which importantly contribute in each cycle of normal walking. These two further pumps are in the calf and unlike the foot pump, are normally muscle-actuated. More specifically, in walking forward, and after weight has been borne on the sole of the foot, the muscles in the upper part of the calf contract to plantarflex the ankle; and, in contracting, these muscles squeeze and empty affected veins, thus operating the proximal venous calf pump. Subsequently, as the leg is swung forward to take another step, the ankle is dorsiflexed to prevent the toes from dragging on the ground, and this action empties the distal calf pump. And finally, as weight is borne once more on the sole of the foot, the venous calf pumps are again primed.